Liquid metal ion gun

ABSTRACT

An emitter of a Ga liquid metal ion source is constituted to include W12 of a base material and Ga9 of an ion source element covering a surface as construction materials. By making back-sputtered particles become elements (W and Ga) of the Ga liquid metal ion sour source, if back-sputtered particles attach to the Ga liquid metal ion source, contamination which may change physical characteristics of Ga9 does not occur. A W aperture is used as a beam limiting (GUN) aperture to place Ga of approx. 25 mg (of melting point of 30° C.) on a surface of a portion included in a beam emission region (Ga store). When emitting ions to the beam limiting (GUN) aperture, Ga in the emission region melts and diffuses on a surface of the beam emission region of the W aperture.

RELATED APPLICATIONS

This application is a continuation of Application 11/312,367 filed Dec.21, 2005, now U.S. Pat. No. 7,211,805, issued May 1, 2007, which is acontinuation of Application 11/004,903 filed Dec. 7, 2004, now U.S. Pat.No. 7,005,651, which claims priority of Japanese Application No.2003-409352 filed Dec. 8, 2003, the contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid metal ion source (LMIS), andmore particularly to an art of making the ion emission of a Ga liquidmetal ion source stable and long life time.

2. Description of the Prior Art

A liquid metal ion gun includes a vacuum chamber in which a liquid metalion source is set, and the liquid metal ion source electricallyinsulated from the vacuum chamber. A high voltage cable capable ofsupplying current between both terminals of the liquid metal ion sourceis connected to the liquid metal ion gun and thereby, it is possible tosupply a high voltage to the liquid metal ion source so as to apply thehigh voltage to the liquid metal ion source appropriately and to heatthe liquid metal ion source by turning on electricity.

It is possible to adjust an ion emission quantity (emission current) byvoltage between the liquid metal ion source and an extract electrode.The emitted ions are received by a beam limiting aperture (gunaperture).

It is important to stably maintain the ion emission of the above Galiquid metal ion source. However, in order to do so, it is necessary tostably supply gallium (hereafter referred to as “Ga”) consumed by theion emission, from a reservoir. A condition in which the emissioncurrent is stable is a condition in which consumption of Ga is balancedwith supply of Ga, that is, a balance equilibrium eutectic condition inwhich Ga is supplied by an amount as consumed for the ion emission.

However, if a foreign material is mixed into Ga, the supply of Ga may beinterrupted, and if the purity of Ga is changed, physical properties arechanged to lose the balance between the consumption and the supply ofGa. Accordingly, the stability of emission becomes deteriorated.

In order to obtain stable emission, it has been constructedconventionally such that an emission ion beam is not directly irradiatedonto an extractor electrode so as not to admix a foreign material intoGa. Further, an electrode (beam limiting aperture) receiving emission ofa beam is constituted by a chemical compound metal of Ga which does notinterrupt supply of Ga even if Ga is subjected to a buildup of acontaminating material due to adhesion of back-sputtered particles ofthe electrode receiving emission of the emission ion beam to Ga, thatis, a metal (Sn or In) not raising the melting point of Ga.

Furthermore, because the number of back-sputtered particles (orparticles causing contamination) to be re-adsorbed to LMIS is decreasedproportionally to the square of the distance between the emitter and thebeam limiting aperture, the distance between the emitter and the beamlimiting (GUN) aperture has been separated.

For example, Japanese Patent Publication No. 3190395 discloses atechnique for constituting a portion irradiated with an ion beam by asintered body in which a low-melting-point metal is infiltrated.JP-A-2001-160369 discloses a technique for, when using common Ga as aliquid metal ion source, using the same kind of Ga as a restrictingmaterial for protection. In addition, JP-A-4-14455 discloses that asurface of an emitter electrode or the emitter electrode is constitutedby one or more of melted metals set to a tip end of the emitterelectrode or metals constituting an alloy.

BRIEF SUMMARY OF THE INVENTION

However, there is no mention about limitation of a construction material(base material) of an aperture in each of the above prior arts.Therefore, when the construction material (base material) of a beamlimiting aperture is exposed by receiving ion emission, a change ofemission stability due to the fact that the base material is sputteredto be mixed in a liquid metal source is not considered.

Even if using the above technique, it is difficult to return theemission which becomes unstable as a result of stably maintaining theemission for a long time to a stable state in a liquid metal ion sourcepreferable to be used for hundreds of hours or more. That is, thedifficulty of recovery when emission becomes unstable has not beenconsidered.

Moreover, when desiring to realize a focused ion beam system for ahigh-current and high-angular-intensity processing beam, it is notpreferable to greatly increase the distance between an emitter and abeam limiting aperture. However, if considering the life time ofcontamination and the beam limiting aperture, it is better to increasethe distance between the emitter and the beam limiting aperture. Thatis, it is found that improving the performance of the focused ion beamsystem and decreasing the contamination of the emitter are in trade-offrelation with each other.

Since a beam limiting aperture is constructed to receive the wholeemission current (2 to 3 μA) of an ion source, the beam limitingaperture becomes thin by sputtering as the ion emission time (=theemission current×the operating time) increases, so that the aperturebecomes expanded. When the expansion of the aperture is started, thebeam current at the downstream side of the beam limiting apertureincreases, and at the same time, a lower electrode is exposed, so thatback-sputtered particles include particles from a lower electrode otherthan those from the beam limiting aperture. It is general that thematerial of the lower electrode is different from that of the beamlimiting aperture. When the back-sputtered particles attach to anemitter, the back-sputtered particles from the lower electrode do notmelt in Ga. Even if the particles melt in Ga, the melting point of theGa rises to prevent the supply of Ga.

Also when constituting the beam limiting aperture from In or Sn metal,there is a problem that the back-sputtered particles attach to theemitter to deteriorate the purity of Ga. If the admixture of In or Sn isup to approx. 10 wt %, the melting point of Ga is lowered. However, ifthe purity of Ga is decreased as a result of accumulation of Sn or Indue to long time use so that the emitter performance is changed, thesupply state of Ga is changed to vary emission.

Hereinafter, problems of a general liquid metal ion gun are morespecifically described by referring to FIG. 3. As shown in FIG. 3, theion gun has a Ga liquid metal ion source 2-1, an extractor electrode 2-2for allowing ions to be discharged, and a beam limiting aperture 2-3.The extractor electrode 2-2 is made of SUS and has an aperture of φ3 mmand an aperture-side wall of a thickness of 1 mm. The distance between atip end of an emitter and the extractor electrode 2-2 is 0.8 mm. Theextractor electrode 2-2 has a structure in which an emission ion beam 7from the liquid metal ion source 2-1 is not directly applied to theextractor electrode 2-2. The extractor electrode 2-2 includes the beamlimiting aperture (GUN) 2-3 therein, and an aperture of φ0.3 mm 2-31 isformed on the extractor electrode 2-2. An aperture made of Sn and havinga thickness of 3 mm is set downward by 5 mm from an upper surface of theextractor electrode 2-2.

The beam limiting aperture 2-3 operates as a restrictor for limitingbeam emission. The extractor electrode 2-2 has a function of applying avoltage between an emitter and the extractor electrode (a space betweenthe emitter and the upper surface of the extractor electrode) to emitthe ions. The extractor electrode 2-2 and the beam limiting aperture 2-3are constituted so that the beam limiting aperture 2-3 is assembled intothe extractor electrode 2-2. Although the aperture 2-3 and the electrode2-2 have the same electric potential, the functions thereof aredifferent.

When providing a voltage difference of approx. 7 kV between the Galiquid metal ion source 2-1 and the extractor electrode 2-2, Ga+ ionsare discharged from the Ga liquid metal ion source 2-1 and applied ontothe beam limiting (GUN) aperture 2-3 made of Sn. The beam limitingaperture 2-3 made of Sn is sputtered by the Ga+ ions, so that Sn atoms(back-sputtered particles 11) are scattered, and some of the atoms arescattered and adsorbed by the Ga liquid metal ion source 2-1.

Further, when the sputtering by the Ga+ ions is advanced, the beamlimiting (GUN) aperture 2-3 is decreased in thickness and increased inaperture diameter, and thereby the beam limiting aperture 2-3 expires inits life time. If using the beam limiting aperture 2-3 beyond its lifetime, the lower electrode of the beam limiting aperture 2-3 is exposed,so that constituent atoms of the electrode material are scattered due tosputtering by the Ga+ ions, and some of the atoms are adsorbed by the Galiquid metal ion source 2-1. The adsorbed substances make the meltingpoint of Ga raise, or directly interrupt a Ga supply flow path to makeemission unstable. If a beam limiting aperture is made of Sn, (theback-sputtered particles of Sn make a compound with Ga to melt in Ga,and the melting point becomes 30° C. or lower up to approx. 10 wt %) Snadsorbed by the Ga liquid metal ion source is melted in Ga, and physicalcharacteristics of Ga such as surface tension and a melting point arechanged depending on the concentration of the solute.

For stable emission of ions, it is preferable that supply of Gacorresponds to the emission and is not changed over time. However, whenthe physical characteristics of Ga are changed, the balance point ischanged, so that an emission current is also changed. Moreover, theemission current is also changed when the flow path of Ga is clogged tochange the supply. quantity of Ga. Therefore, in the case of the generalconfiguration as shown in FIG. 3, it has been difficult to obtain stableemission for a long time, for example, for hundreds of hours.

In view of the above-described problems, objects of the presentinvention are described blow. That is, an object is to stabilizeemission for a long time even if the distance between an emitter and abeam limiting aperture is small. In addition, an object is to extend thelife time of a beam limiting aperture even if receiving sputtering bybeam emission. Further, an object is, when the emission of the liquidmetal ion source becomes unstable, to recover the emission in a stablestate at high reproducibility to use a liquid metal ion source for along time to lengthen the life time thereof. Furthermore, an object isto provide a stable liquid metal ion gun not requiring beam adjustmentof a focused ion beam system.

According to a first aspect of the invention, there is provided a liquidmetal ion gun comprising: a liquid metal ion source having a liquidmetal ion element made of a first metal substrate, a reservoir formed byas second metal substrate for holding the liquid metal ion element, andan emitter formed by the second metal substrate; and a beam limitingaperture formed by a third metal substrate, the beam limiting aperturehaving an aperture for limiting emission of an ion beam extracted fromthe liquid metal ion source, wherein the third metal substrate is formedby a material including the metal substrates constituting the firstmetal substrate and the second metal substrate, respectively. By usingthis liquid metal ion gun, it is possible to decrease the number offactors of contaminating the emitter. The third metal substrateconstituting the beam limiting aperture may be constituted only by thefirst metal substrate and the second metal substrate. Also, the ion gunmay be provided with an acceleration mechanism.

Further, in a liquid metal ion gun comprising: a liquid metal ion sourcehaving a liquid metal ion element made of a first metal substrate, areservoir formed by as second metal substrate for holding the liquidmetal ion element, and an emitter formed by the second metal substrate;and a beam limiting aperture formed by a third metal substrate, the beamlimiting aperture having an aperture for limiting emission of an ionbeam extracted from the liquid metal ion source, it is preferable thatthe beam limiting aperture is formed by a material including the secondmetal substrate, and a supply source of the first metal substrate isarranged in at least a part of a region to which the ion beam issubstantially emitted. By this features, it is possible to easily reducethe above contamination factors.

According to the invention, in fabrication by a large current beam of afocused ion beam apparatus or the like provided with a liquid metal ionsource, it is possible to perform the fabrication with no damage due tothe ion emission around the fabrication. According to the liquid metalion gun of the invention, in a liquid metal ion source having a purposeof using for several hundreds hours or more, it is superior in point ofstably maintaining emission for a long time, and in point of securelyrecovering unstable emission into a stable state, that is, superior ineasiness and reproducibility of recovery of emission stability.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an illustration showing a configuration example of an ion beamapparatus according to an embodiment of the present invention;

FIG. 2 is an illustration showing a configuration of a Ga liquid metalion source;

FIG. 3 is an illustration showing a general liquid metal ion gun;

FIGS. 4A and 4B are illustrations showing a configuration example of aliquid metal ion gun in which a Ga store is arranged, according to anembodiment of the present invention;

FIGS. 5A to 5C are illustrations showing a configuration example of abeam limiting aperture according to an embodiment of the presentinvention;

FIG. 6 is an illustration showing an example of incident angledependency of a sputtering yield of a single-atom solid image pickupdevice; and

FIGS. 7A to, 7C are illustrations showing a configuration example of abeam limiting aperture according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

A liquid metal ion gun according to an embodiment of the presentinvention is described below by referring to the accompanying drawings.A liquid ion gun of the present invention relates to a liquid metal iongun on which a liquid metal ion source and a beam limiting aperture forreceiving emission of ions emitted from the liquid metal ion source aremounted.

Firstly, the whole configuration of an apparatus on which an ion gunaccording to an embodiment of the present invention is mounted isdescribed below by referring to FIG. 1. FIG. 1 is a schematicconfiguration view of an ion beam system using a Ga liquid metal ion gunaccording to an embodiment of the present invention. In FIG. 1,reference numeral 1 denotes an ion beam system, and reference numeral 2denotes an ion gun wherein reference numeral 2-1 denotes an ion source,reference numeral 2-2 denotes an extractor electrode, reference numeral2-3 denotes a beam limiting aperture, reference numeral 2-4 denotesearth ground. Reference numeral 3 denotes a vacuum chamber, referencenumeral 4 denotes a vacuum system, reference numeral 5 denotes an ionpump, and reference numeral 6 denotes a high-voltage power supplywherein reference numeral 6-1 denotes a high-voltage power supply forion acceleration, reference numerals 6-1 a and 6-2 a denote high-voltageconnecting portions, reference numeral 6-2 denotes a high-voltage powersupply for extracting ions, reference numerals 6-3 a and 6-3 b denotehigh-voltage cables, reference numerals 6-4 denotes an ion-sourceheating power supply, reference numeral 7 denotes an emission ion beam,and reference numeral 8 denotes a gate valve provided between the vacuumchamber 3 and the vacuum system 4.

Main operations (functions) of this system are described below. An ionbeam generated by being extracted from the ion source (emitter) 2-1 bythe extractor electrode 2-2 passes through the beam limiting aperture2-3 while diffusion of the beam is limited, and the beam having passedthrough the aperture 2-3 is applied to downstream side by beingaccelerated by the earth ground 2-4. In addition to the aboveconfiguration, by adding functions of thinly restricting a signaldetection system for detecting a signal from an ion beam emission sampleand an emission beam by a lens, and defection-controlling the beam toapply the beam to the sample, it is possible to form a processobservation system.

Next, the configuration and principle of an LMIS are described below.FIG. 2 is an illustration showing the configuration of a liquid metalion source. As shown in FIG. 2, the liquid metal ion source such as theGa liquid metal ion source 2-1 has an needle emitter 2-11 of which tipend is conical, a reservoir 2-12 for storing Ga, a filament 2-13 forturning on power to heat the Ga stored in the reservoir 2-12 and theneedle emitter 2-11, and an insulator base 2-15 for fixing a terminal2-14 for supplying power to the filament 2-13.

The material of the needle emitter 2-11, reservoir 2-12, and filament2-13 is tungsten (W), and Ga is contained in the reservoir 2-12. Thus,elements of a general Ga liquid metal ion source are W, Ga, and aninsulator.

The operation principle about ion emission is that an axis-directionalfield gradient becomes stronger toward an apex since a tip end of theneedle emitter has a conical shape. Ga at a portion near the apex of theneedle emitter is supplied to the emitter apex having a strong electricfield and is shaped in conical, by meand of an electric field stress.Since the apex of the liquid metal has thereby a strong electric fieldof approx. V/Å, ionized potential is lowered, so that field evaporationor field ionization occurs to easily cause ionization. Accordingly, in ahigh voltage electric field of approx. V/Å, ions are discharged into avacuum so that an ion flow occurs.

In accordance with emission of ions, it is necessary to supply Gacorresponding to the discharged quantity of Ga ions. However, because Gabehaves in accordance with liquid flow dynamics, a pressure gradientoccurs so that a surface flow of a continuous fluid is generated. Sincethis flow is in accordance with a Poiseuile's equation for flow due tosurface tension, the flow rate of the flow is changed due to changes ofthe surface tension and viscosity.

In general, pure Ga has a good wetting of a clean tungsten substrate.For example, when a fine groove exists on tungsten, Ga is diffusedthrough the groove due to the capillary phenomenon caused by surfacetension. Further, a needle emitter generally uses a W material having anarrow vertical groove in the axis direction, and thereby it is possibleto diffuse Ga in a reservoir through the groove by the capillaryphenomenon due to the surface tension to supply Ga to a portion near theapex of the emitter. While the stable emission receives Ga correspondingto ion discharge, if surface tension is changed, the supply quantity isalso changed so that the emission is varied.

In the liquid metal ion gun according to this embodiment, a Ga store(which may be referred to as a second Ga supply source if assuming thereservoir as a first Ga supply source) is provided as described below.This configuration is described by referring to FIG. 4A. As shown inFIG. 4A, the emitter 2-11 of the Ga liquid metal ion source 2-1 isconstituted to include, as a construction material, W12 of a substrateand Ga9 of an ion source material covering a surface. In this case, bymaking back-sputtered particles 11 become elements (W and Ga) of the Galiquid metal ion source 2-1, if the back-sputtered particles 11 attachto the Ga liquid metal ion source 2-1, the contamination changingphysical characteristics of the Ga9 does not occur.

That is, a W aperture is used as the beam limiting (GUN) aperture 2-3,and Ga (melting point of 30° C.) of approx. 25 mg is put on a surface ofa portion included in a beam emission region 7-1 (Ga store 10). Whenapplying ions to the beam limiting (GUN) aperture 2-3, Ga in theemission region 7-1 melts and diffuses to the surface of the beamemission region of the W aperture (see FIG. 4B). Therefore, because themelting of Ga and the diffusion of Ga to the emission regionspontaneously occur in accordance with the ion emission, it isunnecessary to previously apply Ga to the W aperture. As a result ofchanging the beam limiting aperture according to this embodiment from ageneral Sn beam limiting aperture to the above beam limiting aperture,it is possible to obtain a stable emission state for 1,200 hours (h).

Next, the aperture of the liquid metal ion gun is described below. Whenusing general gallium as a liquid metal ion source, if assuming thedistance L between the emitter apex of the Ga liquid metal ion gun andthe beam limiting aperture as 7 mm, the mass m of Ga in a Ga store as 25mg, the density ρ of Ga as 5.93 g/cm³, and the ion emission angle α as20°, the aperture radius “r” of the W beam limiting aperture having theGa store is shown by the following formula.r≧m/ρπ(Lα)²In this case, the aperture radius “r” is 0.23 mm.

In the above formula, in the case that the cross section of thethickness of Ga is closed at an aperture portion (see FIG. 5A), this isbecause Ga protrudes from the aperture to a semicircle having thediameter equal to the thickness, and contacts at the opposing portion(see FIG. 5B), in the above condition, when the aperture actually havinga diameter of φ0.3 mm, the aperture is immediately clogged, however, ithas been known that an aperture having a diameter of φ0.6 mm is noteasily clogged (see FIG. 5C). Therefore, a W beam limiting apertureincluding a Ga store having an aperture of φ0.6 mm is used.

Next, the angle dependency of a liquid metal ion gun is described. Theprocessing speed (sputtering yield) by ions has an incident angledependency. FIG. 6 shows a characteristic example about the incidentangle dependency of the sputtering yield. As shown in FIG. 6, when theincident angle θ increases, a cascade occurs at more surface side.Therefore, it increases in accordance with the formula of cos^(−f) θ(f=1 to 2) as shown by the principle of Sigmund. When the incident angleθ increases, the collision efficiency is limited by the shielding effectof adjacent atoms on the surface, and it does not easily pass throughthe surface. Finally, all of the incident ions are reflected almostwithout providing energy for a solid and the yield is suddenlydecreased.

Moreover, in the case of the sputtering phenomenon, because sputteringspeed differs due to the difference between crystal orientations ofcrystal particles, irregularity in which the crystal particle effects asa start point occurs. The surface irregularity is further encouraged dueto the above irregularity and the incident angle dependency of the ionprocessing speed to increase the processing speed, so that the life timeof a beam limiting aperture is shortened. However, the crystal particlediameter of W is approx. 1 μm and the crystal particle diameter of Snregions between 6 and 10 μm. Therefore, the irregularity is not producedon W compared to the case of Sn. Moreover, the sputtering yield issmall. Further, when using a W beam limiting aperture having a Ga storeof the present invention, even if the irregularity of approx. 1 μm isformed, the surface becomes a mirror state because the surface is wettedby Ga, and the sputtering speed is not greatly changed even if using thebeam limiting aperture for a long time.

In addition, since the surface is covered with Ga, even if sputtering ofGa occurs, sputtering of W does not easily occur. The W aperture doesnot subjected to the sputtering as long as Ga does not dry up, and thus,the beam limiting aperture can obtain a desired life time even if the Waperture is thin.

Next, a mounting state of the liquid metal ion gun is described. A Gastore 10 d is formed by placing a lump of Ga on a surface of the W beamlimiting aperture 2-3 having the aperture 2-31, melting the lump, andthen solidifying it by bringing the W beam limiting aperture into asuper cooled atmosphere at −20° C. (see to FIG. 7A). Also, it may bepossible to adopt a configuration obtained by applying Ga10 e to aring-shaped W material or the W sintered body 9 set so as not tointerrupt an ion emission region and putting it on the beam limitingaperture 2-3, or by sandwiching Ga between the ring-shaped W material orW sintered body 9 and the W beam limiting aperture 2-3 (FIG. 7B).Alternatively, by forming a concave portion, a concave groove 2-3-1 orthe like on the surface of the W beam limiting aperture 2-3 in a regionseparated from the aperture 2-31 so that a Ga store 10 f is easilyformed, it is possible to store liquid Ga at a predetermined positioneven if Ga is melted to have fluidity.

W and Ga are good in wetting. However, when W becomes oxidized, it isnot easily wetted. In order to obtain a clean W surface without oxidescum, the W beam limiting aperture is immersed in a hypochlorous acid Nasolution for 1 hr. Alternatively, the surface of the W beam limitingaperture is cleaned through electropolishing using an electrolyticsolution of NaOH or the like, and then ultrasonic-cleaned by deionizedwater.

By mounting the Ga liquid metal ion gun using a W beam limiting aperturehaving a Ga store on a system, when operating the ion gun at an ultimatevacuum degree of the gun of 10⁻⁷ Pa, it is possible to continuously keepa state where an extraction voltage is 7 kV and the emission is 2.4 μAfor 120 hr, and to inhibit, for that time, a beam-focus-like-changewithout performing maintenance such as flashing or emission control.

As described above, when using the W beam limiting aperture of thisembodiment, Ga as a liquid metal ion source is not contaminated even ifGa or W particles sputtered from the beam limiting aperture attach to anemitter. Therefore, even if putting the beam limiting aperture near theGa liquid metal ion source, it is possible to maintain a stable emissionstate for a long period.

Further, according to the W beam limiting aperture of this embodiment,an ion emission region is wetted by Ga, W is not exposed, Ga is mainlysputtered by ion emission, and contamination is not caused even ifback-sputtered particles attach to a liquid metal ion source. As aresult thereof, the emission change is restrained. Moreover, when anelement (W base material) of a beam limiting aperture is exposed byreceiving ion emission for a long time, the W base material may besputtered. In this case, the emission is decreased even if W issputtered and attached to and mixed in Ga liquid metal source, however,since wettabilities of W and Ga are good, W is covered with Ga byflashing (emitter is temporarily heated) and the recovery of emission iseasy.

In addition to this, oxidation of Ga is considered as contamination of aGa liquid metal ion source. However, when the environment clean vacuumis 10⁻⁶ Pa, emission is stable for several days and is decreased inaccordance with advance of the oxidation of Ga because the oxidationalso is advanced at the same time. However, reproducibility of oxidizedGa is improved by performing flashing (heating) at approx. 700° C. forapprox. 30 sec, and it is possible to recover an emission state(emission current, necessary extraction voltage, and stability).

Further, if when the environment clean vacuum is in the order of 10⁻⁷Pa, the emission is stable for several days without changing theemission condition of an extraction voltage or the like, and thus, lensfunctions of an ion optical system are not changed. Therefore, it ispossible to perform ion processing even if focus adjustment is notperformed for several days, and the stability and operability of thesystem are extremely improved.

If a Ga store exists in at least a part in the beam emission region of abeam limiting aperture, Ga is voluntarily diffused in the beam emissionregion of the beam limiting aperture to wet there. Therefore, the beamemission region of the beam limiting aperture becomes a mirror state ofGa free from irregularity. Therefore, the angle dependency of sputteringis minimized and the life time is lengthened. Moreover, sputtering of Gais mainly performed on the surface of the beam limiting aperture, andsputtering of W is almost eliminated. Therefore, it is possible toprovide a long life time even if the beam limiting aperture is thin.

Moreover, when decreasing the beam limiting aperture in thickness, thenumber of beams scattered on a sidewall of the beam limiting aperture isdecreased and thus, it is possible to apply a beam of which direction isaligned with that of energy to the downstream side of the beam limitingaperture. Therefore, in processing by a large current beam of a focusedion beam system, it is possible to perform processing with no damage byion emission around processing. Particularly, according to a liquidmetal ion gun using the W beam limiting aperture of this embodiment, ina liquid metal ion source to be used for hundreds of hours, it issuperior in the point of stably maintaining emission for a long time andin the point of securely recovering unstable emission to stableemission, that is, easiness and reproducibility of recovery of emissionstability.

The present invention is particularly effective when long-timeprocessing is necessary. Moreover, because the maintenance is easy, thepresent invention has a high usability in a large-scale production line.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A liquid metal ion gun comprising: an emitter electrode to whichgallium is supplied; an extract electrode to which a voltage differentfrom that of the emitter electrode is supplied; and a beam limitingaperture having an aperture through which an extracted gallium ionpasses, wherein said beam limiting aperture is formed by arranginggallium on a surface of tungsten.
 2. The liquid metal ion gun accordingto claim 1, wherein said beam limiting aperture includes a ring-shapedtungsten material.
 3. The liquid metal ion gun according to claim 1,wherein said beam limiting aperture includes a sintered body oftungsten.
 4. The liquid metal ion gun according to claim 1, wherein agallium store is provided in at least a part of said beam limitingaperture.
 5. The liquid metal ion gun according to claim 4, wherein saidgallium store exists in a region of said beam limiting aperture, ontowhich region the gallium ion is substantially irradiated.
 6. The liquidmetal ion gun according to claim 4, wherein said gallium store is formedby wetting a surface of said beam limiting aperture with liquid galliumand then solidifying it.
 7. The liquid metal ion gun according to claim4, wherein the opening radius “r” of said beam limiting aperture is setso as to satisfy r≧m/ÿÿ (Lÿ)², wherein “L” is the distance between a tipend of said emitter and said beam limiting aperture, “m” is the mass ofthe gallium in the gallium store, “ÿ” is the density of the gallium, and“ÿ” is an ion emission angle.
 8. The liquid metal ion gun according toclaim 1, wherein a concave portion is formed on a surface of said beamlimiting aperture.
 9. The liquid metal ion gun according to claim 1,wherein a concave groove is formed on a surface of said beam limitingaperture.
 10. The liquid metal ion gun according to claim 1, whereinsaid beam limiting aperture includes the tungsten of which the surfaceis not substantially oxidized.
 11. The liquid metal ion gun according toclaim 1, wherein said beam limiting aperture includes the tungsten whichis immersed in a hypochlorous acid Na solution.
 12. The liquid metal iongun according to claim 1, wherein said beam limiting aperture includesthe tungsten which is electropolished and ultrasonic-cleaned.
 13. Theliquid metal ion gun according to claim 1, wherein said emitterelectrode includes tungsten.